The invention relates in general to gun-launched projectiles and in particular to stabilizing fins for gun-launched projectiles.
Tail fins and tail booms have been used to stabilize non-spinning projectiles. In a large caliber gun system, high projectile velocities and high gas pressures are typical. The high velocities and pressures can be used in several ways to deploy stabilizing fins. Each fin may be configured in such a way that, when the fin exits the constraint of the gun tube, the center of gravity of the fin enables the fin to open (inertia-based deployment). Another deployment method uses the air resistance at muzzle exit to act on a drag feature of the fin to deploy the fin. For shoulder-launched munitions, the projectile may have a relatively low velocity and the known deployment methods may not deploy the fins.
A gas piston deployment system has been used in shoulder-launched munitions. The gas piston mechanism enables the fins to deploy during launch. While the projectile is still in the launch tube, the propellant gases enter the fin boom to charge the gas cylinder. After the projectile exits the launch tube, the pressure surrounding the boom drops, which closes the valve to the gas cylinder. The gas cylinder acts as a piston and moves forward, deploying the fins. The piston presses on the tabs that free the fins to rotate open about the pivot point. When fully deployed, the back end of the fin is forced into a press fit section of the boom to maintain deployment.
Another known deployment method uses a spring for each fin. Each spring opens its respective fin after the fin is free of the launch tube.
Fin deployment for low velocity, shoulder-launched munitions can be complex. In the known gas piston deployment method, tight tolerances are required on an already complex component, the tail boom. Machining the boom is very costly and time consuming. The addition of press fit features to maintain fin deployment is not economical. In some cases, debris from the burning propellant could clog the small valve in the gas piston. The wide range of gun chamber pressures and operational temperatures also introduces variability and uncertainty in gas operated fin deployment.
In the spring-operated deployment method, because each fin has its own spring, the fins may open unevenly. Also, installing individual springs is labor intensive. Importantly, the placement of components on the outermost surface of the projectile introduces undesirable breaks or discontinuities in the smooth contour of the projectile. These breaks in the smooth contours disturb projectile flight and significantly increase drag.
A need exists for a fin deployment mechanism for a relatively low velocity projectile.